Various cardiovascular, neurosurgical, pulmonary and other interventional procedures, including repair or replacement of aortic, mitral and other heart valves, repair of septal defects, pulmonary thrombectomy, coronary artery bypass grafting, treatment of aneurysms, and neurovascular procedures, may require general anesthesia, cardiopulmonary bypass, and arrest of cardiac function. In order to arrest cardiac function, the heart and coronary blood vessels must be isolated: from the remainder of the circulatory system. Using current techniques, isolation of the heart and coronary blood vessels is accomplished by placing a mechanical cross-clamp externally on the ascending aorta downstream of the ostia of the coronary arteries, but upstream of the brachiocephalic artery. A catheter is then inserted directly into the ascending aorta between the cross-clamp and the aortic valve, and cardioplegic fluid is infused through the catheter into the ascending aorta from which it flows into the coronary arteries to perfuse the myocardium. An additional catheter may be introduced into the coronary sinus for retrograde perfusion of the myocardium with cardioplegic fluid. In addition, the myocardium is usually cooled by irrigating with cold saline solution and/or application of ice or cold packs to the heart. Cardiac contractions will then cease.
While the heart is stopped, circulation is maintained throughout the body by a cardiopulmonary bypass system. A venous cannula is placed in a major vein such as the inferior vena cava in order to withdraw deoxygenated blood from the body. The deoxygenated blood is directed to a blood oxygenator which restores the blood with oxygen, and the oxygenated blood is pumped back into a major artery downstream of the aortic cross-clamp through an arterial return cannula.
Although the patient is on cardiopulmonary bypass, a certain amount of blood not withdrawn through the venous cannula returns through the venous system to the heart. In addition, cardioplegic fluid delivered into the coronary arteries drains back into the heart through the coronary sinus. Therefore, the heart must be vented to prevent an excessive quantity of blood and other fluids from pooling in the heart while it is not beating. To accomplish this, a venting cannula may be introduced through the aortic wall into the aorta upstream of the cross-clamp to withdraw fluid from the aortic root. Alternatively, a venting cannula may be introduced through a wall of the pulmonary artery near the point at which it connects to the right ventricle of the heart to allow blood to be withdrawn from the pulmonary artery. In procedures in which the heart itself is surgically opened, a venting cannula may be introduced directly into the heart through the incision in the heart wall.
Known techniques for performing major surgeries such as coronary artery bypass grafting and heart valve repair and replacement have generally required open access to the thoracic cavity through a large open wound, known as a thoracotomy. Typically, the sternum is cut longitudinally (a median sternotomy), providing access between opposing halves of the anterior portion of the rib cage to the heart and other thoracic vessels and organs. An alternate method of entering the chest is via a lateral thoracotomy, in which an incision, typically 10 cm to 20 cm in length, is made between two ribs. A portion of one or more ribs may be permanently removed to optimize access.
In procedures requiring a median stemotomy or other type of thoracotomy, the ascending aorta is readily accessible for placement of an external cross-clamp, and for introduction of a cardioplegic fluid delivery cannula and venting cannula through the aortic wall. The pulmonary artery is exposed as well to allow introduction of a venting catheter through the pulmonary arterial wall. However, such surgery often entails weeks of hospitalization and months of recuperation time, in addition to the pain and trauma suffered by the patient. Moreover, while the average mortality rate associated with this type of procedure is about two to fifteen per cent for first-time surgery, mortality and morbidity are significantly increased for reoperation. Further, significant complications may result from such procedures. For example, application of an external cross-clamp to a calcified or atheromatous aorta may cause the of release of emboli into the brachiocephauc, carotid or subclavian arteries with serious consequences such as strokes.
Methods and devices are therefore needed for isolating the heart and coronary arteries from the remainder of the arterial system, arresting cardiac function, venting the heart, and establishing cardiopulmonary bypass without the open-chest access provided by a median sternotomy or other type of thoracotomy. In particular, methods and devices are needed which facilitate venting the heart sufficiently to allow the heart to be placed under cardioplegic arrest with full cardiopulmonary bypass, without requiring open-chest access to the heart and without requiring an incision or puncture in the aorta, in the pulmonary artery, or in the heart wall.
The descriptive, terms downstream and upstream, when used herein in relation to the patient's vasculature, refer to the direction of blood flow and the direction opposite that of blood flow, respectively. In the arterial system, downstream refers to the direction further from the heart, while upstream refers to the direction closer to the heart with the opposite true in the venous system. The terms proximal and distal, when used herein in relation to instruments used in the procedure, refer to directions closer to and farther away from the operator performing the, procedure